| <html lang="en"> |
| <head> |
| <title>Remote Non-Stop - Debugging with GDB</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="Debugging with GDB"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Remote-Protocol.html#Remote-Protocol" title="Remote Protocol"> |
| <link rel="prev" href="Notification-Packets.html#Notification-Packets" title="Notification Packets"> |
| <link rel="next" href="Packet-Acknowledgment.html#Packet-Acknowledgment" title="Packet Acknowledgment"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| Copyright (C) 1988-2019 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software'' and ``Free Software Needs |
| Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,'' |
| and with the Back-Cover Texts as in (a) below. |
| |
| (a) The FSF's Back-Cover Text is: ``You are free to copy and modify |
| this GNU Manual. Buying copies from GNU Press supports the FSF in |
| developing GNU and promoting software freedom.'' |
| --> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Remote-Non-Stop"></a> |
| <a name="Remote-Non_002dStop"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Packet-Acknowledgment.html#Packet-Acknowledgment">Packet Acknowledgment</a>, |
| Previous: <a rel="previous" accesskey="p" href="Notification-Packets.html#Notification-Packets">Notification Packets</a>, |
| Up: <a rel="up" accesskey="u" href="Remote-Protocol.html#Remote-Protocol">Remote Protocol</a> |
| <hr> |
| </div> |
| |
| <h3 class="section">E.10 Remote Protocol Support for Non-Stop Mode</h3> |
| |
| <p><span class="sc">gdb</span>'s remote protocol supports non-stop debugging of |
| multi-threaded programs, as described in <a href="Non_002dStop-Mode.html#Non_002dStop-Mode">Non-Stop Mode</a>. If the stub |
| supports non-stop mode, it should report that to <span class="sc">gdb</span> by including |
| ‘<samp><span class="samp">QNonStop+</span></samp>’ in its ‘<samp><span class="samp">qSupported</span></samp>’ response (see <a href="qSupported.html#qSupported">qSupported</a>). |
| |
| <p><span class="sc">gdb</span> typically sends a ‘<samp><span class="samp">QNonStop</span></samp>’ packet only when |
| establishing a new connection with the stub. Entering non-stop mode |
| does not alter the state of any currently-running threads, but targets |
| must stop all threads in any already-attached processes when entering |
| all-stop mode. <span class="sc">gdb</span> uses the ‘<samp><span class="samp">?</span></samp>’ packet as necessary to |
| probe the target state after a mode change. |
| |
| <p>In non-stop mode, when an attached process encounters an event that |
| would otherwise be reported with a stop reply, it uses the |
| asynchronous notification mechanism (see <a href="Notification-Packets.html#Notification-Packets">Notification Packets</a>) to |
| inform <span class="sc">gdb</span>. In contrast to all-stop mode, where all threads |
| in all processes are stopped when a stop reply is sent, in non-stop |
| mode only the thread reporting the stop event is stopped. That is, |
| when reporting a ‘<samp><span class="samp">S</span></samp>’ or ‘<samp><span class="samp">T</span></samp>’ response to indicate completion |
| of a step operation, hitting a breakpoint, or a fault, only the |
| affected thread is stopped; any other still-running threads continue |
| to run. When reporting a ‘<samp><span class="samp">W</span></samp>’ or ‘<samp><span class="samp">X</span></samp>’ response, all running |
| threads belonging to other attached processes continue to run. |
| |
| <p>In non-stop mode, the target shall respond to the ‘<samp><span class="samp">?</span></samp>’ packet as |
| follows. First, any incomplete stop reply notification/‘<samp><span class="samp">vStopped</span></samp>’ |
| sequence in progress is abandoned. The target must begin a new |
| sequence reporting stop events for all stopped threads, whether or not |
| it has previously reported those events to <span class="sc">gdb</span>. The first |
| stop reply is sent as a synchronous reply to the ‘<samp><span class="samp">?</span></samp>’ packet, and |
| subsequent stop replies are sent as responses to ‘<samp><span class="samp">vStopped</span></samp>’ packets |
| using the mechanism described above. The target must not send |
| asynchronous stop reply notifications until the sequence is complete. |
| If all threads are running when the target receives the ‘<samp><span class="samp">?</span></samp>’ packet, |
| or if the target is not attached to any process, it shall respond |
| ‘<samp><span class="samp">OK</span></samp>’. |
| |
| <p>If the stub supports non-stop mode, it should also support the |
| ‘<samp><span class="samp">swbreak</span></samp>’ stop reason if software breakpoints are supported, and |
| the ‘<samp><span class="samp">hwbreak</span></samp>’ stop reason if hardware breakpoints are supported |
| (see <a href="swbreak-stop-reason.html#swbreak-stop-reason">swbreak stop reason</a>). This is because given the asynchronous |
| nature of non-stop mode, between the time a thread hits a breakpoint |
| and the time the event is finally processed by <span class="sc">gdb</span>, the |
| breakpoint may have already been removed from the target. Due to |
| this, <span class="sc">gdb</span> needs to be able to tell whether a trap stop was |
| caused by a delayed breakpoint event, which should be ignored, as |
| opposed to a random trap signal, which should be reported to the user. |
| Note the ‘<samp><span class="samp">swbreak</span></samp>’ feature implies that the target is responsible |
| for adjusting the PC when a software breakpoint triggers, if |
| necessary, such as on the x86 architecture. |
| |
| </body></html> |
| |
